On the origin of the kinematic distribution of the subparsec young stars in the Galactic center

Within a half-parsec from the Galactic center ( GC), there is a population of coeval young stars that appear to reside in a coherent disk around amassive black hole. Surrounding this dynamically cool stellar system, there is another population of stars with a similar age and much larger eccentricities and inclinations relative to the disk. We propose a hypothesis for the origin of this dynamical dichotomy. Without specifying any specific mechanism, we consider the possibility that both stellar populations were formed within a single disk some 6 +/- 2 Myr ago. But this orderly structure was dynamically perturbed from the outside in by an intruding intermediate-mass black hole or a dark cluster with amass of similar to 10(4)M circle dot. We suggest that, under the action of dynamical friction, this perturber migrated inward to similar to 0.15-0.3 pc from the GC. Along the way, it captured many stars in the outer disk region into its mean motion resonance, forced them to migrate with it, excited their eccentricity and inclination, and engaged them in close encounters. However, stars in the inner regions of the disk retain their initial coplanar structure. Our simulations show that a perturber on a low-inclination or overhead orbit to the disk plane can lead to the observed kinematic properties of these young stars, albeit it is unlikely to produce the controversial two-disk structure. We predict that some of the inclined and eccentric stars surrounding the disk may have similar values of the galactocentric semimajor axis, and precision determination of their orbits will provide a test for this hypothesis, as well as evidence for a dark companion around the massive black hole at the GC.Astronomy & AstrophysicsSCI(E)0ARTICLE2919-93366